1. Field of the Invention
The present invention relates generally to electronic packaging, and more particularly to multi-chip modules (“MCMs” or “MCM”) for light emitting devices such as light emitting diodes (“LEDs”) and the like.
2. Description of the Related Art
With the advent of LEDs and other light emitting devices of increased brightness and color fidelity, multi-chip lighting modules have become available to further increase luminous flux output. MCMs for lighting typically comprise a single package with a plurality of LEDs, although it is understood that other light emitting devices may be used. Since these MCMs comprise a plurality of light emitting devices, they generally allow for high output of light emission. However, a common problem with light emitting devices such as LEDs is the emitted light from the device chip is largely non-directional and non-uniform, which can negatively impact the emission and optical efficiency of a MCM.
In an attempt to combat this problem, U.S. Patent No. 2004/0080939 discloses a light emitting device with multiple light sources generally mounted on a substrate. Pads of conductive and reflective materials are mounted on the substrate, with the reflective materials used to improve the emission properties of the multiple light sources. A lens is also provided to cover the light sources, which aims to further improve the emission properties of the multiple light sources. However, for some of these devices the overall efficiency may be compromised since some of the light emitted from the multiple light sources can be absorbed is different device structure such as the substrate and spaces between the conductive and reflective pads.
International Patent No. WO 2006/054228 attempts to solve the efficiency problem of multiple-chip lighting modules by providing a substantially continuous reflective layer so less light is absorbed into structures such as the substrate or into the spaces between conductive and/or reflective regions. However, it is well-known that multi-chip modules and many other types of electronic packages, whether containing integrated circuits or discrete components such as diodes or power transistors, discharge sufficient heat to require thermal management. The objective of thermal management in the design of electronic packaging is to maintain the operating temperature of the active circuit or junction side of the component low enough (for example, 110° C. or below) to prevent premature component failure. Various cooling strategies including conduction heat transfer are in common use. One conventional way of implementing conduction heat transfer for dissipating heat in an electronic package is to allow the heat to conduct away along the leads of the device. However, the leads often do not have sufficient mass or exposed surface area to provide effective heat dissipation. For example, high intensity light emitting diodes (LEDs) that emit light principally in the visible part of the electromagnetic spectrum can generate significant amounts of heat that are difficult to dissipate using such conventional techniques.
The devices of both U.S. Patent No. 2004/0080939 and International Patent No. WO 2006/054228 generate sufficient heat to require thermal management. The conductive layers provided in both devices are generally insufficient to handle the necessary thermal management to prevent premature component degradation or failure, and additional means of heat dissipation, such as heat sinks, are required. Heat sinks, however, generally take up space and increase the thickness of such devices, which can be problematic in applications in which space is at a premium.